Barnett's esophagus is found in about 10% of patients who seek medical care for heartburn (gastroesophageal reflux or “GERD”), and is considered to be a premalignant condition associated with esophageal cancer. Barrett's esophagus refers to an abnormal change (metaplasia) in the cells of the lower end of the esophagus, which is believed to be caused by damage from chronic stomach acid exposure (reflux esophagitis). Barrett's esophagus is marked by the presence of columnar epithelia in the lower esophagus that replaces the normal squamous cell epithelium. The columnar epithelium is better able to withstand the erosive action of the gastric secretions; however, this metaplasia confers an increased cancer risk of the adenocarcinoma type. The metaplastic columnar cells may be of two types: gastric, which are similar to metaplastic stomach cells (technically not Barrett's esophagus), and intestinal, which are similar to metaplastic cells found in the intestines. A biopsy of the affected area will often contain a mixture of both cell types. Intestinal-type metaplasia confers a higher risk of malignancy, and is usually identified by locating goblet cells in the epithelium.
Both high and low (“cryogenic”) temperature tissue ablation treatments are currently offered for treating Barrett's esophagus. As used herein, “tissue ablation” refers to the necrosis, destruction or killing of tissue cells, which may be accomplished using a number of different energy delivery modalities for achieving high or low temperature cell necrosis. By way of one example, U.S. Pat. No. 7,150,745 discloses a system for ablating esophageal tissue by positioning an expandable balloon probe in the area of the esophagus to be treated, the balloon exterior being plated with a large number of surface electrodes that can be selectively activated to convey bi-polar radio frequency electrical energy into the esophageal surface tissue for destroying the Barrett's cells. By way of further examples, U.S. Pat. Nos. 6,027,499, and 7,025,762 disclose cryogenic ablation systems for directly spraying esophageal wall tissue with liquid nitrogen. Cryogenic balloon instruments and systems for (non-ablative) treatment of blood vessel wall tissue are disclosed and described in U.S. Pat. No. 6,468,297 and in U.S. Patent Application Publication No. 20060084962. The foregoing U.S. Pat. Nos. 7,150,745, 6,027,499, 7,025,762 and 7,081,112, and U.S. Patent Application Publication No. 20060084962 are each incorporated herein by reference for all that they teach and disclose.
The objective of these tissue ablation therapies is to destroy the characteristic Barrett's columnar epithelium layer, without causing unwanted damage to underlying submucosa tissue or surrounding healthy tissue. In particular, the columnar epithelium characteristic of Barrett's esophagus has been reported to reach lengths of up to 8 cm, and is approximately 500 microns thick. Disruption of deeper tissues in the muscularis mucosae, located at a depth of approximately 1000 microns or deeper, can lead to stricture formation and severe long term complications. On the other hand, missed or buried “islands” of Barrett's cells can result if the therapy does not uniformly encompass all affected tissue areas. Thus, precise control of both the ablation tissue surface area and “kill depth” are highly desirable.